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1-to-6 analog buffer

A T Rajesh Kumar
Prodigy 140 points
Other Parts Discussed in Thread: TLV4110, TLV4112, TLV4111

Hi,

My requirement is that I need to accept a signal between 1-100 KHz, and supply it on 6 output ports. In short, I am looking for a 1-to-6, or at least 1-to-2 analog output drive buffer. Can someone suggest a suitable part for me.

thanks and regards,

rajesh

  • 0
    TI__Guru* 93105 points

    Hi A T,

    • What are the characteristics of the input signals i.e. voltage levels, waveform types, termination requirements, etc?
    • What are the buffer output requirements in terms of voltage swing, current and loads?
    • Do you plan to use single, or dual supplies, and what levels?
    • What package type do you plan to use in the application require?
    • Can multiple devices be used to provide the 1-to-6 buffer function?
    • Are there any critical electrical, thermal, or physical requirements?

    Regards, Thomas

    PA - Linear Applications Engineering

  • 0 in reply to Thomas Kuehl
    Prodigy 140 points
    Hi Thomas,
    Thanks for the response. Here are the answers:

    What are the characteristics of the input signals i.e. voltage levels, waveform types, termination requirements, etc?
    The signal is an AM sine wave, 10V p-p, coming on 50 ohm cable.

    What are the buffer output requirements in terms of voltage swing, current and loads?
    The swing required is 5V p-p. Current on each output port should be max of 100mA.

    Do you plan to use single, or dual supplies, and what levels?
    Dual Supplies, -5V, +5V.

    What package type do you plan to use in the application require?
    Any package.

    Can multiple devices be used to provide the 1-to-6 buffer function?
    Yes.

    Are there any critical electrical, thermal, or physical requirements?
    None.

    regards,
    rajesh
  • 0 in reply to A T Rajesh Kumar
    TI__Guru* 93105 points

    Hi A T,

    See the comments I have added to your responses. I have a couple more questions before I can make recommendations: 

    What are the characteristics of the input signals i.e. voltage levels, waveform types, termination requirements, etc?
    The signal is an AM sine wave, 10V p-p, coming on 50 ohm cable.

    You mention in the next comment that the output voltage is 5 Vp-p. Are you planning on reducing the 10 Vp-p input signal to bring it down the 5 Vp-p level before it is applied to the buffer inputs? Or, are you planning on dividing down the output down to 5 Vp-p? 

    What are the buffer output requirements in terms of voltage swing, current and loads?
    The swing required is 5V p-p. Current on each output port should be max of 100mA.

    Is the output load located right after the buffers, or will they be located some distance down a 50 ohm cable?

    Do you plan to use single, or dual supplies, and what levels?
    Dual Supplies, -5V, +5V.

    Do realize that op amps do have limitations regarding their linear input and output swing ranges relative to the supply voltage. You mention 5 Vp-p at the output so +/- 5 V supplies will be fine for that output level. However, the 10 Vp-p input might be a problem with +/-5 V supplies. Is there any possibility of increasing the supply levels?

    Regards, Thomas

    PA - Linear Applications Engineering

  • 0 in reply to Thomas Kuehl
    Prodigy 140 points
    Hi Thomas,
    Sorry for the late response. Please find answers below:

    You mention in the next comment that the output voltage is 5 Vp-p. Are you planning on reducing the 10 Vp-p input signal to bring it down the 5 Vp-p level before it is applied to the buffer inputs? Or, are you planning on dividing down the output down to 5 Vp-p?
    We will bring it down (using resistor divider) to 5 Vp-p before it is applied to the buffer inputs. After that we will convert it to 0-5 V signal using the drive op-amps. It is really a pain to use dual supplies, especially since we will be deriving those supplies from +12V of motherboard PCIe slot.

    Is the output load located right after the buffers, or will they be located some distance down a 50 ohm cable?
    The load will be located around 2 feet away down a 50 ohm SMA cable.


    Do realize that op amps do have limitations regarding their linear input and output swing ranges relative to the supply voltage. You mention 5 Vp-p at the output so +/- 5 V supplies will be fine for that output level. However, the 10 Vp-p input might be a problem with +/-5 V supplies. Is there any possibility of increasing the supply levels?
    Now that we have decided to use 0-5 V signal, this is also answered.

    regards,
    rajesh
  • 0 in reply to A T Rajesh Kumar
    TI__Guru* 93105 points

    Hi Rajesh,

    An issue that you are will run into using a single 5 V supply is that no op amp's output is going to be able to drive all the way to the supply rails. The extent to which they will swing becomes more limited as the output current is increased. If you bias the op amp non-inverting input at +2.5 V and apply a 2.5 Vpk signal via capacitive coupling, the input would swing from 0 V to 5 V. The output has a limited swing range and it won't be able to swing from 0 to 5 V. Clipping will occur at the peaks as they near the rails. 

    In your application information you mention a 100 mA-pk current to ground. When using a single +5 V supply the output will be required to deliver very little through the load when the input and output are at 0 V. Therefore, in that case the output will swing within millivolts, or tens-of-millivolts, of ground. But as the output moves more positive, the output current will increase and then at some level begin to limit. Just how close it gets to the positive rail depends on the op amp output characteristics. 

    The one op amp option that I came up with is the TLV4110. It can easily supply the required output current. If you need to swing to 5 Vpk, then I would power it from a +5.5 to +6 V supply. Its slew rate is just on the edge of what is needed to pass a 100 kHz signal without producing significant slew rate distortion. You can find the datasheet here:

    Regards, Thomas

    PA - Linear Applications Engineering

  • 0 in reply to Thomas Kuehl
    Prodigy 140 points
    Hi Thomas,
    Thanks for the response. I will be powering it with +12V of PCIe motherboard slot.
    Are you aware of any op-amp with more than 2 outputs.
    regards,
    rajesh
  • 0 in reply to A T Rajesh Kumar
    TI__Guru* 93105 points

    Hi Rajesh,

    It is uncommon for a power op amp to have more than one, or two, channels in a single package. It is a matter of thermal management. I do not know of any op amp products that supply high output current where there is more than two channels. Do keep in mind the thermal requirements of any amplifier you chose to use in your application. Most power op amp datasheets provide helpful information and guidance regarding the amplifier's thermal considerations.

    You mention that you plan to power the output buffer with a +12 V supply. Should you decide to try the TLV4111 single, or TLV4112 dual, the recommended maximum supply voltage is 6 V. Therefore some kind of linear, or buck/boost, regulator would be needed to bring the 12 V level down to 5.5 to 6 V.

    Regards, Thomas

    PA - Linear Applications Engineering